The invention concerns an ignition coil for a combustion engine with a cylindrical primary coil body carrying a primary winding, a low voltage connection area for connection of the primary coil to a low voltage, a secondary coil inductively coupled with the primary coil, for providing a high voltage for a spark plug of the combustion engine, whereby the secondary coil is carried on a secondary coil body that is concentrically enclosed by the primary coil body, a high voltage connection area, in which the secondary coil contacts the spark plug, whereby the secondary coil body encloses a cylindrical magnetic core, and the primary coil body and the secondary coil body are both enclosed by an electrically and magnetically conductive tube, whereby the tube includes a longitudinal slot therethrough, as well as a method for the production thereof.
An ignition coil of this type is disclosed in DE 100 57 567. Of these types of ignition coils, the invention concerns the so-called “bar coils for ignition components of combustion engines”, which include a long design, whereby they can be positioned in the available narrowly bordered space within the combustion engine. A primary voltage fits on the primary coil over the low voltage connection area, which, because of the inductive coupling between primary and secondary coils, is available as high transforming voltage on the high voltage connection area of the secondary coil and there meets the spark plug. With known ignition coils is provided a magnetic circuit through the primary and secondary coils as well as the cylindrical magnetic core and the magnetically conductive tube. To reduce eddy current losses in the also electrically conductive tube, a longitudinal slot is disposed therethrough, so that the induced electrical eddy currents are minimized.
Because of the demands placed on the ignition coil, it is necessary to wind the primary coil several times on the primary spool body that surrounds the secondary coil. With an even number of coil layers, both leads of the primary coil extend from the same end of the primary spool body, so that a direct connection of the low voltage lead can be achieved there. If, however, the number of coil layers is uneven, the coil leads extend from opposite ends of the primary coil body, which means one of the coil leads must be led back from the opposite side to the low voltage connection area. In practice, the primary coil is required to have an uneven number of coil layers, for example three. Because of the required electrical parameters of the ignition coil, a two layer coil is often insufficient, whereas a four layer primary coil would result in too large of a coil diameter.
With the ignition coils known in the art, feed back of the coil lead is achieved by including a groove on the interior of the primary coil body, within which the lead is led back. This does disadvantageously feature that this groove on one hand provides a mechanical weak point of the ignition coil and on the other hand, the electromagnetic field about the lead has a disadvantageous effect on the physical properties of the ignition coil. Another solution known in the art provides that the electrical lead back is achieved through a flat leader, for example in the form of a foil, which stretches along the cylindrical surface of the primary spool body. This solution is also unsatisfactory with respect to the mechanical properties, expensive with respect to the manufacturability and fraught with risk.